Like you, I have the camera for the job, but perhaps not the skill. I'm good with clear air photography but I always botch the underwater stuff somehow, at least in streams. Got some good pictures snorkeling in the Carribean but that's been it.
One is clear water. We see water and think it's clear, but when you're trying to look any sort of distance under water, even the slightest tint shows up. Our streams aren't swimming pools. And to make matters worse, my fishing location choices tend to seek out a touch of color, as those times at those places are usually better fishing!
Also, related to clear water: Even if the water is clear, you very often make it not so by wading! Of course you can't stop yourself from stirring up some silt. So, how to avoid it? Well, in a slower pool, I'm not sure there's a good way short of getting a pole and lowering the pole in without wading. Low amounts of current means the silt goes every direction farther than arms reach. In faster water, make sure you take the pictures upstream of you. But it can't be too fast, or all you'll see is a lot of white bubbles in your picture.
If it has an underwater mode, it's far superior than other settings.
Unless you stick your face under with it, it's very tough to aim underwater. So forget the zoom, stick with wide angle, point and pray.
Positioning fish is a lot easier if you control the fish by handling the line, NOT by touching the fish. It's still tricky.
